Absorption dryer

ABSTRACT

The invention relates to an absorption dryer having a new type of contact device, viz. a contact device including at least one fabric structure, whose threads are such that they can absorb and convey a liquid drying agent and whose apertures are adapted to let through humid gas, whereby the contact between the humid gas and the drying agent occurs essentially radially in respect of the threads, the drying agent preferably being in the plane of the fabric structure and the gas perpendicular thereto through the apertures.

TECHNICAL FIELD

The present invention relates to a new absorption dryer adaptedespecially to dry humid gas, especially humid air. In other words, theinvention relates to the technical field in which the humid gas iscontacted with a liquid drying agent, such that the drying agent absorbsmoisture from the gas at issue. The drying agent is then regenerated,i.e. relieved of the absorbed moisture, and is again used in the dryer.The novelty of the invention is a drastically simplified and improvedconstruction of the contact means for establishing contact between thehumid gas and the liquid drying agent. Moreover, the invention relatesto this new contact means itself.

BACKGROUND OF THE INVENTION

The absorption dryer is one of several types of dryer. Two otherimportant types are the adsorption dryer and the condenser dryer. Theadsorption dryer operates with a solid drying agent, which is usuallyregenerated with the aid of electrically heated hot air. The adsorptiondryer frequently consists of a fabric structure similar to corrugatedfibreboard and impregnated with a drying agent. This structure usuallyis in the form of a rotor, and the humid air is blown through the flutesand dehumidified. The drying agent can be regenerated by a sector of therotor being reserved for the regenerating function. The sector is sealedin some suitable manner on both sides of the rotor, and hot air is blownthrough the rotor material which at that very moment is located in thesector. The advantage of such an adsorption dryer is that it candehumidify down to low relative moisture contents, since solid dryingagents, as a rule, have very low vapour pressures of equilibrium withwater vapour in, for instance, air. 10-30% RH thus is quite possible toachieve in exit air, but if supply air is not too humid, suitably notexceeding 50-60% RH.

Although the adsorption dryer must be considered relatively simple inrespect of design, it must, however, comprise a driving motor and acomparatively complex rotor. Its great disadvantage is, however, itslack of operation economy. By operation economy is meant the powerrequirements in kWh per kg of removed water. 1.2-1.5 kWh per kg of wateris reasonable for an adsorption dryer. The theoretical powerrequirements are about 0.75 kWh per kg of water. The reason for thelosses in the adsorption dryer is that the rotor, during its continuousrotation between the cold and the warm sector, consumes a considerableamount of power during the exchange of heat. Moreover, the adsorptiondryer is not very convenient at high moisture contents and temperatures,or when large amounts of water are to be removed, such as in the case ofdamage by water or in operating situations in moist and warm climates,including laundry rooms. A further disadvantage of the adsorption dryeris that it is difficult to exchange the heat of warm and humidregeneration air in an inexpensive fashion. In other words, a gas/gasheat exchanger is necessary, and therefore usually just the warm andhumid regeneration air is released outdoors. Otherwise, by heatexchange/condensation of moisture it is possible to recover the suppliedpower as heat, thereby avoiding wall ducts.

The condenser dryer, is built more or less like an ordinaryrefrigerating or freezing machine. Humid air is dehumidified bycontacting the cold surface of the evaporator. The condenser dryer hasgood operation economy and can process air having a high moisturecontent and a high temperature. The supplied power remains in the room,and humid hot air need not be wasted outdoors. However, the condenserdryer suffers from the drawback that a compressor having a driving motoris necessary. In continuous operation, the life of the most expensivecomponents of the dryer will be just about a year. A further drawback ofthe condenser dryer is that it contains FREON fluorocarbon, which, as iswell known, is a much discussed substance these days from theenvironmental point of view. Besides, the condenser dryer is relativelyexpensive, possibly excluding the smallest orders of size, which can usecomponents manufactured in very large series for the refrigeratorindustry.

The absorption dryer requires good phase contact between a liquid dryingagent and the humid gas. This can be accomplished in a number of ways. Acommon technique is to establish such phase contact in a columncontaining fillers. As a rule, the drying agent is sprayed over thecolumn packing at the head of the column, while the humid air isintroduced countercurrently at the bottom of the column. A problem incolumns is that it is difficult for this construction, owing to itsgeometry, to dispose of the heat of reaction by thermal radiation. Infact, considerable amounts of heat are generated when water vapour fromthe humid gas is absorbed in the liquid drying agent, which besides alsoapplies to the adsorption dryer. A higher operating temperature andlower efficiency must thus be accepted, since efficiency decreases asthe operating temperature rises. Alternatively, refrigerating coils canbe arranged in the column packing, or the liquid drying agent can beremoved at several levels, then be cooled and be fed back again. Anothertechnique of avoiding too great a rise in temperature is to use highlyintensive pumping-around of the drying agent through the column andthrough an external cooler. Part of this flow is then concentratedcontinuously in a boiler.

A further common construction is based on the spray-drying technique. Afine mist of the liquid drying agent encounters the humid aircountercurrently in a tubular reactor. In this construction, it will bevery difficult to have the dry exit air completely free from droplets ofthe drying agent, and moreover the thermal problems are the same as inthe preceding case.

A third variant of the absorption dryer is a contact means having thestructure of corrugated fibreboard, flutes extending in two directionsperpendicular to each other, the material being permeable to liquid butimpermeable to gas. The liquid drying agent can be sprinkled on a bodyof the material so as to flow down through the vertical flutes, and aircan be injected through the remaining horizontally oriented flutes. Alsoin this case the thermal problems or restrictions as mentioned abovewill appear. Otherwise, the principle uses the condition of concentratedliquid drying agent permeating the walls of the air flutes, encounteringhumid air and absorbing water, which diffuses towards a moreconcentrated drying agent solution in the adjoining drying agent flutes.This technique, however, has its limitations, viz. a limitation of thediffusion of the wall material in the corrugated structure. Thegeometric interface per unit of volume will also be relatively small,which results in a low capacity per unit of volume of corrugated contactmaterial.

SUMMARY OF THE INVENTION

In the light of what has been discussed above, the main object of thepresent invention is to provide a new design of an absorption dryer, inwhich the thermal radiation of the heat of reaction is good, i.e. theincrease in temperature in the contact material is small, and thediffusion paths for the reactants, i.e. water vapour and liquid dryingagent, at the point of reaction in the contact material are short. Afurther object of the invention is to provide a design which is simpleand, thus, reliable and inexpensive to manufacture and to service.Further objects of the invention will be obvious to those skilled in theart from the more detailed description of the invention that followsbelow.

More specifically, the invention relates to an absorption dryer of thetype which is adapted especially to dry humid gas, humid air of coursebeing the most common field of application in practice. The term "humid"is besides to be understood in a wide, general sense, since theinventive principle is of course also applicable to a case in which agas is "humid" with some liquid other than water.

The main components of the absorption dryer according to the inventionare the same as those of an absorbent dryer of prior-art type, viz.means for supplying the humid gas, means for supplying a liquid dryingagent, contact means for establishing contact between the humid gas andthe liquid drying agent, such that the drying agent absorbs moisturefrom said gas, and means for regenerating the liquid drying agent forrenewed use in the dryer. The objects of the invention are, however,achieved by a special structure and design of the solid materialconstituting the reaction surface between the humid gas and the liquiddrying agent, and therefore the following description of the inventionwill in the first place be directed to the design and function of thecontact means at issue. The remaining means included in the dryer willbe slightly touched upon when certain concrete embodiments of theinvention will be elucidated, but basically these means are constructedin the same manner as before and also have the same function as beforeand therefore need not be described in more detail here.

Moreover, the inventive dryer can of course include further optionalcomponents, which are per se known and thus need not be elucidated here.Some of these further optional components will, however, be discussedbelow in the description of concrete embodiments.

The novelty of the absorption dryer according to the invention is thatthe contact means for establishing contact between the humid gas and theliquid drying agent comprises at least one fabric structure orfabric-like structure, whose threads, which may have a yarn-likestructure, are of such a nature that they can absorb and convey theliquid drying agent after being soaked therewith via the means forsupplying the liquid drying agent and whose apertures are adapted to letthrough the humid gas, which is introduced via the means for supplyingthereof, whereby the contact between the humid gas and the drying agentoccurs essentially radially in respect of the threads in said structure,the drying agent preferably being in the plane of the fabric structureand the gas perpendicular thereto through said apertures.

In the present case, the term fabric structure is used in the generallyrecognised meaning for fabric or woven fabric, i.e. basically a fabricmade from yarn by weaving and usually characterised in that in two ormore systems of threads, which intersect at a constant angle, eachthread winds in a plane over and under other threads. This, of course,represents the basic composition of the fabric structure, which does notnecessarily mean that crossing at a constant angle must always occur,although regular stitches are of course preferred. Thus, a variety ofcarpet structures, e.g. of the type wall-to-wall carpet with open pileor uncut pile, as well as knitted and crochet structures can be used.

Besides, the term fabric means that most cases concern one- ortwo-dimensionally determined goods having low flexural rigidity and suchconnection as to allow handling in the spread state.

A structure corresponding to the fabric structure can, however, beachieved without any actual weaving, i.e. without the threads runningover and under each other. Thus, it may also be a matter of afabric-like structure, which is frequently designated e.g. nonwovenmaterial or nonwoven fabric. In such a material, the mesh apertures inthe woven structure must, of course, be equivalent to apertures providedin said nonwoven fabric in some way or another. These apertures can beprovided for instance by through perforations in a bonded material.

Finally, it should be added that, although this will probably beindirectly apparent to those skilled in the art, the term thread and thelike is in the present case used in a wide sense and is frequently to beplaced on a level with yarn or an accumulation of fibres, for instanceas present in a nonwoven product of the Chifonet® type (between twoneighbouring apertures therein). This meaning is in itself generallyaccepted since use is often made of the term thread to designate yarnwhen considered to be an individual object.

Expressed in another way and including certain preferred embodimentsthereof, the specific structure and design of the contact means in thedryer according to the invention can be summarised as follows. The solidstructure of the contact means consists of a fabric structure which,seen in relation to the geometrical surface, is relatively thin and inwhich the liquid drying agent flows through the structure, while humidgas is blown or sucked therethrough in a direction which issubstantially perpendicular to the flow of the drying agent andperpendicular to the surface of the structure. The important thing ofthe invention is the intimate and repetitive, finely divided contactwhich is accomplished between the drying agent and the humid gas owingto the drying agent in the threads of the fabric structure beingextremely easily accessible to the humid gas. They may be said to beexposed all around, which means that the diffusion paths in the liquidphase will be extremely short. Diffusion does not occur in the directionof a plane as in a corrugated structure according to prior-arttechnique, but substantially circularly, concentrically around eachfibre or accumulation of threads between two neighbouring apertures.This accumulation may be of circular cross-section, if the fabricconsists of yarn, and of square or rectangular cross-section in the caseof perforated nonwoven fabric and the like. In all cases, the structureis thin, almost two-dimensional in a layer of the contact material.

Further it is extremely important that the pressure drop is small in anabsorption dryer. In fact, a pressure drop consumes power and, besides,there is a greater risk that droplets of the drying agent are entrainedby the passing air if the pressure drop is great. The contact meansaccording to the present invention can be given such a design that aminor pressure drop arises. For optimum structure, the fabric shouldtherefore not be so close that the liquid drying agent, under the actionof capillary forces and the wetting tendency of the fabric material,forms a coherent film across the entire surface. In that case, thepressure drop will be unreasonably great, and if gas should in any casebe blown through such a structure, the waste of drying agent will begreater. The liquid phase forms bubbles, which burst, whereby the dryingagent is entrained by the air. Liquid drying agents are often viscous,and therefore the tendency of blocking the apertures in a fabricstructure is considerable. Moreover, the fabric or the fabric-likestructure should be dimensioned such that the number of apertures arenot too few per unit area or too large, since in that case the humid gasdoes not get the necessary close contact with the fibres wet with thedrying agent. Besides, the fabric should have a sufficient totalcross-sectional area to allow the required amount of drying agent to beconveyed. This amount is of the same magnitude as the expected waterabsorption owing to generally known physical data. This is a consequenceof the fact that the moisture-absorbing capacity of the drying agentdecreases as the concentration falls, i.e. as the water absorptionincreases. Thus, it must be seen to it that the apertures of the fabricfor the humid gas are both sufficiently frequent and, for preventingwetting/film formation over the apertures, sufficiently large. It maythen be easy to reach a deadlock, viz. a relatively rough structure, inwhich the fibres are collected in skeins and there are relatively largeopenings between the skeins, in which case these thick skeins make thedrying agent "have time to" flow away without being exposed to the humidair to the extent desired. Sufficiently large apertures in the fabricresult, as stated above, in the contact with the humid gas being poor.It will therefore be necessary to reach a compromise between on the onehand the desire for small air holes and thin skeins of fibres, bothoccurring frequently, and, on the other hand, the desire for a large,liquid-conveying cross-sectional area and the requirement that the gasapertures not be clogged. The compromise is necessary since a certaindrying capacity per unit area is required. It would otherwise bepossible to operate with a very large fabric for a small air flow, sincein that case the pressure drop would be small even if the pores weresmall and the cross-sectional area of the fabric would be sufficient.

An important and fundamentally distinguishing feature of the dryeraccording to the invention and a dryer having the corrugated structureas described above is best elucidated when observing a small surfaceelement of the drying agent contact means of the two dryers. In a dryeraccording to the invention, the contact between the humid gas and thedrying agent occurs essentially "radially" in respect of the threads andpreferably substantially in cross-flow, the drying agent being in theplane of the fabric and the gas perpendicular thereto, i.e. through theapertures. In the corrugated structure, the flow is also a cross-flow,but both flows being in the plane, or rather on both sides of aseparating wall in the plane.

As will be obvious from that stated above, a preferred embodiment of theinventive dryer is represented by the case in which the fabric structureor the fabric-like structure is a well-balanced compromise between thedesire for thin threads, the desire for small air holes, and the desirefor a close frequency of threads and holes. These three desires, whichall promote a good and efficient phase contact, a condition of a goodcapacity, should, however, be adapted to the requirement for a large,liquid-conveying cross-sectional area, which otherwise easily becomesthe capacity-restricting factor, and the requirement that the holes forthe gas not be blocked by the liquid drying agent at the pressure dropsthat may be accepted. The above-mentioned requirements act in theopposite direction compared with the above-mentioned desires, viz.towards thicker threads and larger air holes, resulting in a lowerfrequency of both holes and threads. Such a compromise still beingpossible, with a layer of fabric or fabric-like material, is shown anddescribed in an embodiment below, a common scouring cloth acting ascontact means.

Another embodiment of the invention is represented by the case in whichthe contact means is arranged substantially vertically in the dryer,such that the drying agent flows from the top downwards through thestructure under the action of gravitation and capillary forces throughthe fabric, while the means for supplying the humid gas is arranged toblow or suck the gas substantially horizontally, i.e. substantiallyperpendicular to the flow of drying agent.

A further preferred embodiment of the invention is represented by thecase in which the threads are composed of fibres of a hydrophilicmaterial, when the drying agent usually is an aqueous solution of somedrying agent which is per se known, for instance lithium chloride.Although the invention is not restricted to a special dimension of thethreads in a respect other than expressed functionally, as mentionedabove regarding the function of the dryer, a preferred average dimensionof the threads at issue is in the range of 0.1-10 mm, particularly inthe range of 0.5-2 mm.

Nor is the mesh or the size of the apertures critical in absolutefigures, since as mentioned above the function is the primary thing inthe context, but a preferred range for said apertures is 0.25-10 mm,particularly 0.5-2.5 mm. By apertures is, of course, in most cases meantthe side edge of the apertures, especially if the apertures at issueusually are square, or otherwise generally the diagonal of the aperture.

The case of a single layer of fabric in the contact means doesfrequently not represent the optimum case. Thus, the contact meansusually comprises a plurality of separate fabric structures orfabric-like structures, which should then be separated by spacing means.The separation is necessary in practice, since several fabric layers, asmentioned above arranged one above the other, would otherwise sticktogether, such that the majority of the apertures would be blocked byneighbouring layers of fabric. The probability of the aperturescoinciding, i.e. lying one above the other, is in fact almostnon-existent. As spacing means, use is preferably made of anintermediate netting having a mesh size greater than that of the fabricstructure or the fabric-like structure. Such a plastic netting makes thepermeability to air excellent in all layers of fabric. Practicalexperiments have shown that the pressure drop will be very small and isproportional to the number of layers of fabric. The great advantage ofseveral layers of fabric is the fact that the cross-sectional area ofthe liquid-conveying fibres can be made sufficiently large despite alarge aperture area and without necessitating collection of the fibresin thick skeins. Moreover, practical experiments have shown that thedrying capacity is approximately proportional to the number of layers offabric, at least up to 10 layers. As a non-restrictive example of aspacing netting, mention can be made of a plastic netting having largemeshes, for instance one of the Engtex make, which is a knitted plasticnetting having a mesh size of 5×5 mm.

The above described design of the contact means according to theinvention results in a sufficient cross-sectional area of theliquid-conveying fibres at a reasonable size of the contact means.Besides, use can be made of a sufficiently thin fabric, such that thecontact between the liquid drying agent and the humid gas becomesefficient while the relatively large apertures offer a desirably smallpressure drop of the gas and counteracts the risk of clogging. Byarranging a plurality of fabric structures in several layers separatedby intermediate spacing means, and the fact that the apertures inneighbouring fabric layers do not, in all probability, lie one above theother, the air is compelled to pass through the structure in a zigzag.This in turn makes the contact between the wet fibres and the humid gasin the fabric layers at issue more efficient. The advantage of several,separated thin fabrics is, in addition to a sufficient totalcross-sectional area for the liquid phase and a sufficient total openarea for the gas, that the capacity is fairly constant along the heightof the contact means. This is a consequence of the gas being sucked orblown in cross-flow through the fabric layers, while the liquid dryingagent is supplied to the fabric layers at the upper horizontal edgesthereof (when vertically arranged). In the upper part of the contactmeans, the gas has already been dehumidified after passing one or a fewindividual fabric layers. The solution in these layers is consumedrelatively quickly, and therefore these innermost fabric layers do notyield the same good dehumidification further down in the structure. Onthe other hand, the drying agent in the outer fabric layers is hardlyused at all since the gas is already dehumidified, but this drying agentis of use only when it reaches down a distance in the contact means,where it encounters non-dehumidified gas. This can be readily expressedas the reaction zone being moved outwards as the distance from the topincreases. If the dimensions are exactly correct, the reaction surfacesshould therefore be farthest out at the bottom of the dryer.

However, it should be noted in this context that, although in thespecified case the fabric structure consists of several layers, itshould still be a thin structure, among other things to make it easierfor the heat of reaction to radiate.

If a single layer of fabric or fabric-like structure should, in anindividual case, prove to be insufficient, this need not necessarilyimply that a construction must be applied having a number of separatefabric structures, one arranged above the other. Within the scope of theinvention, it will thus also be possible to weave, or provide in someother fashion, complex fabric structures or fabric-like structures, forinstance having a plurality of different kinds of threads or threadthicknesses of different materials and having different wettingproperties, thereby obtaining a fabric structure which results inexcellent performance with a single layer of fabric. An embodiment ofthe contact means is represented by the case in which this consists of afolded fabric structure of one layer of fabric. The gas being blown orsucked substantially perpendicular to or through the fabric also appliesto this case of a folded fabric, if the folded structure is regarded ascontact means.

Instead, the idea behind the invention can be generally expressed suchthat the contact means is a single or complex fabric, in one or morelayers, having such a scattered and fine-threaded pore system for theliquid drying agent that thick films or streaks of liquid do not form.The apertures or the pore system for the humid gas must, however, besufficiently scattered or have sufficiently large pores, therebypreventing capillary forces in coaction with the wetting tendency of thematerial from causing blocking of the gas pores with the liquid phase.Further the apertures must occur frequently.

Even if the threads or fibres of the fabric preferably are made of ahydrophilic material as mentioned above, this does not exclude the useof a fabric of some hydrophobic material, whereby the gas aperturescould be allowed to be smaller and, thus, more in number, which in turnwould result in a more efficient fabric, without increasing the risk ofblocking of the gas pores. One might also imagine that a fabric whichactually has too fine pores in respect of the risk of blocking of thegas pores or apertures could, by impregnation with some hydrophobicmaterial, be given quite different properties with improved gaspermeability in its wet state. This is, however, just one of a pluralityof various possibilities of developing a suitable fabric structure. Asindicated above, the invention thus is not restricted to a specificfabric or fabric structure.

The fabric structure need not necessarily be arranged as a freelyhanging cloth or the like. A preferred embodiment can in some casesinstead be represented by the case in which the fabric structure isformed as a cylinder. Such a cylinder is preferably arranged upright,i.e. its main axis extending substantially vertically. Such anarrangement has been found practical in, for instance, drying capacitiesof up to some twenty or thirty kg of water per hour. In the event ofgreater capacities, the diameter or height can, however, beimpractically great. A solution to this problem may, for instance, be anarrangement of the fabric in a plurality of substantially parallelplanes with partition walls or spacing means, and means for supplyinggas and means for ejecting gas and supply of the drying agent at theupper edge.

As an example of the capacity of a dryer according to the invention itmay be mentioned that a scouring cloth of common consumers' quality,having a woven yarn-like structure with threads/yarn having a diameterof 1-2 mm and apertures of about the same size at a surface of 15 dm²,resulted in a water absorption of 300 g/h at a relative humidity of 75%and at an air flow of 75 m³ /h. The scouring cloth was arranged as acylinder having a diameter of 16 cm and a length/height of about 60 cm.The humid air was blown in through one end wall and left radiallythrough the cloth, while 40% lithium chloride in an amount of about 500g/h was flushed over the scouring cloth from above. It should be addedthat this example does not in any way represent the optimum case, butintends only to exemplify an extremely simple but still relativelyefficient dryer according to the invention, having a layer of relativelythick fabric and, consequently, in this simple structure, relativelythick skeins and large apertures for the gas. The pressure drop of thegas/air was 16 mm water column, which is the greatest possible pressuredrop with reasonable fans, and therefore a fabric of this type is notconvenient in multilayer-designs of the contact means.

As a non-restrictive example of a fabric material for use in the contactmeans according to the invention, the fabric which is commerciallyavailable under the trademark Chifonet can be mentioned, i.e. theproduct which is normally used as scouring cloth. Such a productrepresents a fabric-like structure with holes or apertures, whichconstitute about 50% of the fabric surface. A preferred range of thepercentage of apertures or holes in a fabric structure or fabric-likestructure according to the invention in general can be 10-90%,especially 30-70%. As an example of a dryer according to the inventionwith a thin non-woven product of the type stated above, it may bementioned that this yields the same water absorption under the sameconditions as in the scouring cloth case above, however, at a pressuredrop of the gas, which cannot even be measured. Such a fabric thus isperfect in a multilayer-arrangement for higher capacity.

As mentioned above, the inventive dryer comprises, in addition to thenew contact means, means for supplying the humid gas, means forsupplying the liquid drying agent, and means for regenerating the dryingagent at issue for renewed use in the dryer. These means are per seknown in the context of drying and therefore need not to be described inmore detail here. What may possibly be added is that the means forsupplying the drying agent should, of course, be a suitable means whichfeeds and distributes the drying agent uniformly or homogeneously overthe fabric-like structure, preferably at the upper edge thereof in avertical arrangement.

The inventive dryer may also, if required, comprise one or more of thefollowing components which are previously known: condenser for utilisingthe heat of steam formation from the means (boiler) for regenerating thedrying agent; one or more pumps for respectively diluted and regenerateddrying agents; one or more fans for blowing or sucking the gas throughthe contact means and optionally through the condenser; a heat exchangerbetween hot, regenerated drying agent from the regenerating means andcold, diluted drying agent from the contact means; and an additionalcooler for the drying agent before the contact means. The constructionand function of these additional optional components will be well knownto those skilled in the art and will therefore not be described in moredetail here.

In a second aspect, the invention relates to the new contact meansitself, i.e. a contact means adapted to be used in an absorption dryer,the contact means being distinguished by comprising at least one fabricstructure or fabric-like structure, whose threads are of such a naturethat, after being soaked with a liquid drying agent, they can absorb andconvey the drying agent, and whose apertures are adapted to let throughhumid gas, for instance humid air, whereby the contact between the humidgas and the drying agent is adapted to occur essentially radially inrespect of the threads in said structure, the drying agent preferablybeing in the plane of the fabric structure and the gas perpendicularthereto through said apertures.

To the preferred embodiments of the new contact means according to theinvention, the same features apply as discussed above in connection withthe new absorption dryer according to the invention, and therefore theseembodiments need not be repeated once more.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be elucidated in more detailwith reference to the accompanying drawing. FIG. 1 illustrates anabsorption dryer according to the invention.

DETAILED DESCRIPTION

An absorption dryer according to the illustrated preferred embodimentincludes the following components:

1. Contact means

2. Pump

3. Pump

4. Additional cooler

5. Heat exchanger

6. Boiler

7. Condenser

8. Fan

9. Distribution device

The figure also shows the following flows:

A: Humid supply air

B: Outlet water

C: Dry exit air

The function of this specific embodiment of the inventive dryer can bedescribed as follows.

The contact means 1 of the invention consists in this case of 10 layersof Chifonet fabric with intermediate layers of a spacing netting of theEngtex make, said netting having a mesh of about 5×5 mm. In this case,the contact means is formed as an upright cylinder having a diameter of20 cm and a height of 16 cm. The wall thickness is about 9 mm.

Humid air is sucked in through the circumferential surface of thecontact means (arrows designated A) by the negative pressure produced bythe fan 8. The air flow is about 200 m³ and the negative pressure about10 mm water column. The pump 3 feeds concentrated lithium chloride tothe distribution device 9, which in this case is a perforated hose inthe form of a circle having the same diameter as the contact means. Thisresults in the upper horizontal edge of all the fabric layers beingsoaked with the solution. The pump 3 sucks concentrated, hot (about 140°C.) solution from the boiler 6. This is a glass jar having a volume ofabout 5 l and a built-in immersion heater and thermostat.

On its way to the pump 3, the distribution device 9 and the contactmeans 1, the solution passes first a heat exchanger 5 and then anadditional cooler 4. The concentrated lithium chloride must berelatively cool when reaching the contact means, on the one hand becausethen it absorbs moisture better (the lower the temperature) and, on theother hand, because the polymeric plastic materials of the contact meansusually do not withstand a temperature exceeding about 70° C. The heatexchanger 4 is a small laboratory cooler made of glass. The flow amountsto about 6 l/h. Heat exchange is effected against the cold diluted flowof the dryer, as will be described below. After passing through the heatexchanger 5, the concentrated flow still has a somewhat too hightemperature, about 60° C., and is therefore cooled to about 30° C. bymeans of an additional cooler 4, which here is an about 3-m-long, narrowpolyethylene hose arranged in front of the suction side of the fan 8.This position is, however, not to be seen in the Figure.

On its way down through the contact means, the concentrated solutionabsorbs water from the air. The solution becomes slightly warmer, about40° C., depending on the heat of reaction, despite the powerfulsucking-through of air. The volume of the solution then increases fromabout 6 l/h to about 9 l/h.

The cold diluted flow from the dryer is sucked via the pump 2 from acollecting vessel (not shown) in connection with the contact means andis conveyed through the heat exchanger to the boiler. The heat exchangerhas the double function of cooling the warm flow as mentioned above,while transferring some of the heat to the boiler. The cold dilutedsolution is now preheated to about 80° C. before reaching the boiler.This increases the efficiency of the dryer to a considerable extent. Inthe boiler, the solution is regenerated by boiling away water, which inthe shown case occurs in an amount of 3 l/h. The power of the heater is2200 Watt which represents a power requirement of barely 0.8 kWh/kg ofwater absorbed from the air. This can be compared with, for instance, avalue of 1-1.5 kWh/kg of water as a common value for commerciallyavailable dryers.

The water vapour is then condensed in a condenser 7, which in this caseis a small (20×20×5 cm) standard-type condenser as used in cryogenicengineering. It goes without saying that it is not necessary to condensethe water vapour, but since in most cases one wants to utilise the heatin the form of the supplied electrical energy for heating the space inwhich the dryer operates, this is a simple technique. It may here alsobe added that the purpose of a dryer of the invention is relativelysimple, viz. condensing pure water vapour and not a mixture of air andwater vapour, such as is the case of the regeneration air fromadsorption dryers. It is worth noticing that in some cases one wouldobtain a net cooling in a space owing to the evaporation/drying, if theheat of condensing was not utilised.

In the present case, it constitutes an additional advantage that thesame fan, which is a simple axial fan, manages the conveyance of airthrough both the contact means and the condenser owing to the fact thata small pressure drop could be given to both of them. Besides, the pumpsare of a simple, inexpensive and reliable type, viz. so-calledoscillation pumps.

Finally, the designations B and C schematically illustrate the removedwater in the liquid state and the warm, dehumidified exit air,respectively. The conditions in the exemplified case was an airtemperature of 22° C. and a relative humidity of 80%.

I claim:
 1. An absorption dryer for drying humid gas with a liquiddrying agent, comprising:means for supplying a humid gas; means forsupplying a liquid drying agent; contact means for establishing contactbetween the humid gas and the liquid drying agent such that the dryingagent absorbs moisture from the gas; means for regenerating the liquiddrying agent for renewed use in the dryer the contact means including atleast one fabric structure, the fabric structure having threads thatabsorb and convey the liquid drying agent after being soaked therewithvia the means for supplying the liquid drying agent, the fabricstructure having apertures that let through the humid gas introduced viathe means for supplying the humid gas, the apertures being so frequentand so large as to prevent wetting and film-forming over the apertures,wherein the contact means establishes contact between the humid gas andthe drying agent such that contact occurs essentially radially relativeto the threads in the fabric structure, and the drying agent is disposedin a plane of the fabric structure and the humid gas is supplied by themeans for supplying the humid gas perpendicular to the plane of thefabric structure and passes through the apertures.
 2. The absorptiondryer as claimed in claim 1, wherein the threads of the fabric structureare sufficiently spaced and are sufficiently thin to prevent formationof films of the liquid drying agent in the thread network and over theapertures.
 3. The absorption dryer as claimed in claim 1, wherein thethreads are composed of fibers of a hydrophilic material.
 4. Theabsorption dryer as claimed in claim 1, wherein the contact means isarrange, substantially vertically in the dryer, such that the dryingagent flows from a top of the contact means downwards through the fabricstructure under the action of gravitation and capillary forces throughthe fabric structure, and the means for supplying the humid gas isarranged to force the humid gas substantially horizontally.
 5. Theabsorption dryer as claimed in claim 4, wherein the supply means for thedrying agent is is disposed relative to the contact means such that itsupplies the drying agent at an upper edge of the contact means.
 6. Theabsorption dryer as claimed in claim 1, wherein the threads have adimension in the range of 0.1-10 mm.
 7. The absorption dryer as claimedin claim 1, wherein the apertures have a dimension in the range of0.25-10 mm.
 8. The absorption dryer as claimed in claim 1, wherein thefabric structure is a cloth.
 9. The absorption dryer as claimed in claim1, wherein the contact means includes a plurality of separate fabricstructures separated by spacing means in the form of intermediatenetting having a greater mesh than a mesh of the fabric structure. 10.The absorption dryer as claimed in claim 1, is in the form of acylinder.
 11. The absorption dryer as claimed in claim 1, wherein apercentage of apertures in the fabric structure is 10-90% of an area ofthe fabric structure.
 12. The absorption dryer as claimed in claim 1,wherein the contact means includes a folded fabric structure.
 13. Acontact means for an absorption dryer, comprising:at least one fabricstructure the fabric structure having threads that are adapted to absorband convey a liquid drying agent after being soaked therewith and havingapertures that are adapted to let through a humid gas, the aperturesbeing sufficiently frequent and large to prevent wetting andfilm-forming over the apertures, wherein, in use, contact between thehumid gas and the drying agent occurs essentially radially relative tothe threads of the fabric structure, and the drying agent is disposed ina plane of the fabric structure and the humid gas is supplied in adirection substantially perpendicular to the fabric structure and passesthrough the apertures.
 14. The absorption dryer as claimed in claim 2,wherein the threads are composed of fibers of a hydrophilic material.15. The absorption dryer as claimed in claim 2, wherein the contactmeans is arranged substantially vertically in the dryer, such that thedrying agent flows from a top of the contact means downwards through thefabric structure under the action of gravitation and capillary forcesthrough the fabric structure, and the means for supplying the humid gasis arranged to force the humid gas substantially horizontally.
 16. Theabsorption dryer as claimed in claim 4, wherein the threads have adimension in the range of 0.1-10 mm.
 17. The absorption dryer as claimedin claim 4, wherein the apertures have a dimension in the range of0.25-10 mm.
 18. The absorption dryer as claimed in claim 4, wherein thefabric structure is a cloth.
 19. The contact means of claim 13, whereinthe threads of the fabric structure a resufficiently spaced and aresufficiently thin to prevent formation of films of the liquid dryingagent in the thread network and over the apertures.